Informational Article
Medical Billing and Coding:
Process, Challenges & How They Connect
Medical billing and coding are two linked functions that convert a documented patient encounter into paid revenue. Medical coding translates the clinical record into standardized ICD-10-CM, CPT, and HCPCS Level II codes. Medical billing takes those codes, builds a claim, submits it to the payer, and manages adjudication, denials, appeals, and patient balances until the account is resolved.
The two functions connect at four handoff points: charge capture, code assignment, claim edits, and denial feedback. Coding errors surface as billing denials, and billing denials are only permanently fixed by correcting the coding or documentation behind them. A practice that treats coding and billing as separate silos will keep re-appealing the same denial category every month.
Both disciplines run on code sets that change every year. The FY 2026 ICD-10-CM update, effective October 1, 2025, added 487 new diagnosis codes, revised 38, and deleted 28. The CPT 2026 code set, effective January 1, 2026, carried 418 changes in total, made up of 288 new codes, 84 deletions, and 46 revisions, with new entries covering areas such as remote physiologic monitoring, augmented intelligence services, and a rebuilt lower extremity revascularization section. Any practice still billing from last year's code list is generating denials it does not need.
This guide explains what medical coding is, which code sets exist, how the coding process works, exactly where coding hands off to billing, what the most common errors and challenges are, which certifications matter, and how audits fit into the picture.
What Is Medical Billing and Coding?
Medical billing and coding is the combined administrative discipline that turns clinical documentation into a compliant, payable insurance claim. Coding provides the standardized language, billing provides the financial transaction, and together they form the operational core of the revenue cycle.
In a small practice, one person often performs both roles. In larger groups and billing companies, the roles separate: certified coders review documentation and assign codes, while billers handle claim creation, submission, remittance posting, denial work, and patient balances. The separation improves accuracy and audit defensibility, but it only works when a structured feedback loop sends denial data back to the coding team.
What Is Medical Coding?
Medical coding is the process of reviewing clinical documentation and assigning standardized alphanumeric codes that describe the patient diagnosis, the services performed, the supplies used, and the circumstances that affect payment.
Coding serves three purposes at once. It communicates clinical facts to the payer in a machine-readable format, it establishes medical necessity for the service billed, and it feeds population health, quality reporting, and risk adjustment data. Because the same code drives payment, compliance, and quality scoring, coding accuracy is not only a billing concern.
What Are the Main Medical Code Sets?
The main medical code sets are ICD-10-CM, ICD-10-PCS, CPT, HCPCS Level II, CDT, NDC, DRG, APC, revenue codes, and place of service codes. Each set answers a different question on the claim.
ICD-10-CM
Patient diagnoses, symptoms, and reasons for the encounter
All claim types; establishes medical necessity
ICD-10-PCS
Inpatient hospital procedures
Institutional inpatient claims only
CPT
Physician and outpatient procedures and services
Professional and outpatient facility claims
HCPCS Level II
Supplies, drugs, DME, ambulance, and non-physician services
Professional, DME, and facility claims
CDT
Dental procedures
ADA dental claim form and 837D
NDC
Specific drug product, manufacturer, and package
Pharmacy claims and provider-administered drug reporting
MS-DRG
Inpatient case grouping for payment
Inpatient hospital reimbursement
APC
Outpatient payment classification
Hospital outpatient prospective payment
Revenue codes
Facility department or cost center
UB-04 and 837I claims
Place of service codes
Physical setting where the service was delivered
CMS-1500 and 837P claims
Modifiers
Circumstances that alter a service without changing its definition
Attached to CPT and HCPCS codes
Modifiers deserve separate attention because they cause a disproportionate share of denials and audit findings. Modifier 25 identifies a significant, separately identifiable evaluation and management service on the same day as a procedure. Modifier 59 and the X-series modifiers identify distinct procedural services. Modifiers 26 and TC split professional and technical components. Laterality modifiers such as RT, LT, and 50 identify the side treated. Using a modifier to bypass an edit rather than to describe a documented clinical fact is the single fastest way to attract a payer audit.
How Does the Medical Coding Process Work?
The medical coding process works by reading the complete encounter documentation, identifying every billable and reportable element, assigning the most specific codes supported by that documentation, and validating the code combination against coding guidelines and payer edits before the claim is created.
1. Review the Complete Clinical Documentation
The coder reads the full note, including chief complaint, history, examination, assessment and plan, procedure notes, operative reports, pathology results, medication administration records, and any addenda. Coding from a problem list or a superbill checkbox alone is a common source of both undercoding and unsupported coding.
2. Identify the Diagnoses and Assign ICD-10-CM Codes
Diagnosis coding follows the ICD-10-CM Official Guidelines for Coding and Reporting, including sequencing rules, laterality, episode of care for injuries, combination codes, and Excludes1 and Excludes2 instructions. Codes must be assigned to the highest level of specificity the documentation supports; an unspecified code is legitimate only when the record genuinely lacks the detail, not as a shortcut.
3. Identify the Services and Assign CPT and HCPCS Codes
Procedure coding matches what was actually performed and documented. For evaluation and management services, level selection is based on medical decision-making or total time on the date of the encounter under the current E/M guidelines. For procedures, the coder confirms approach, extent, laterality, and whether the service is included in a global surgical package or separately reportable.
4. Apply Modifiers and Check Edits
The coder applies modifiers supported by the documentation, then validates the code set against National Correct Coding Initiative procedure-to-procedure edits, medically unlikely edits, global period rules, add-on code requirements, and payer-specific coverage policy. This validation step is what turns a technically correct code list into a claim that will survive adjudication.
5. Query the Provider When Documentation Is Insufficient
When documentation is ambiguous, conflicting, or incomplete, the coder issues a compliant provider query that presents the clinical facts and asks for clarification without leading toward a higher-paying answer. Queries and their responses become part of the record and are reviewed in audits, so template wording matters.
6. Finalize and Release Charges
Once codes and modifiers are validated, charges are released to the billing team with units, dates of service, place of service, and any authorization references. Delays at this step directly extend days in accounts receivable, so coding turnaround time should be tracked as a revenue cycle metric, not just a productivity metric.
How Do Medical Billing and Coding Connect?
Medical billing and coding connect at four operational handoffs, and each handoff is a place where revenue is either protected or lost.
What Is the Difference Between Medical Billing and Medical Coding?
The difference between medical billing and medical coding lies in the input, the output, and the counterpart each role deals with. Coding starts with the clinical record and produces codes; billing starts with codes and produces payment.
| Attribute | Medical Coding | Medical Billing |
|---|---|---|
| Primary input | CodingClinical documentation and the medical record | BillingAssigned codes, patient demographics, and insurance data |
| Primary output | CodingICD-10-CM, CPT, and HCPCS code assignments | BillingSubmitted claims, posted payments, and resolved balances |
| Core question answered | CodingWhat was done and why | BillingWho pays, how much, and when |
| Main counterpart | CodingThe provider and the medical record | BillingThe payer, the clearinghouse, and the patient |
| Key risk | CodingUpcoding, undercoding, and unsupported coding | BillingDenials, timely filing loss, and aged accounts receivable |
| Common credentials | CodingCPC, CCS, COC, CRC, CCA, RHIT | BillingCPB and payer or software-specific training |
| Main performance measure | CodingCoding accuracy rate and audit pass rate | BillingClean claim rate, denial rate, and days in A/R |
What Are the Common Challenges in Medical Billing and Coding?
The common challenges in medical billing and coding are documentation gaps, annual code set changes, modifier misuse, medical necessity denials, payer policy variation, staffing shortages, and technology fragmentation.
Incomplete or non-specific documentation
a service that is performed but not clearly documented cannot be coded to the level it deserves, and unspecified diagnosis codes weaken medical necessity support.
Annual code set churn
hundreds of ICD-10-CM and CPT changes each year mean encounter forms, EHR favorites lists, charge masters, and scrubber rules all need updating on schedule.
Modifier misuse
modifiers 25 and 59 are among the most audited elements in professional billing, and using them to force a payment rather than describe a clinical fact creates recoupment exposure.
Unbundling and NCCI edit conflicts
billing component procedures separately when a comprehensive code exists triggers edits and, if systematic, compliance findings.
Upcoding and downcoding
upcoding creates fraud exposure, while chronic downcoding quietly erases legitimate revenue and is rarely detected without an internal audit.
Medical necessity denials
a service can be correctly coded and still denied when the diagnosis does not meet the payer coverage policy or local coverage determination.
Payer policy variation
the same code can require different modifiers, documentation, or authorization at three different payers in the same market.
Staffing and certification gaps
experienced coders are scarce, and turnover directly degrades accuracy and turnaround time.
Disconnected systems
when the EHR, practice management system, clearinghouse, and reporting tools do not reconcile, missing charges and unposted remittances go unnoticed for months.
How Do You Reduce Medical Coding Errors?
Reducing medical coding errors requires a repeatable prevention system rather than case-by-case correction after denials arrive.
Run internal coding audits on a fixed schedule
sample charts per provider per quarter, score accuracy, and share results with the provider directly.
Update code sets on time
implement ICD-10-CM changes by October 1 and CPT changes by January 1 across the EHR, encounter forms, charge master, and scrubber rules.
Maintain a payer policy library
document each major payer's rules for modifiers, authorization, frequency limits, and documentation, and review it at least twice a year.
Use a compliant query process
standardize non-leading query templates and retain query records with the chart.
Track denials by reason code and by provider
a denial trend tied to one provider is a documentation training issue, while a trend tied to one payer is a policy issue.
Invest in clinical documentation improvement
short, targeted provider feedback on specificity, laterality, and time documentation pays back faster than any additional appeal capacity.
Verify scrubber rules quarterly
an outdated edit library gives false confidence that claims were checked when they were not.
What Certifications Do Medical Billers and Coders Need?
Certification is not legally required to work in medical billing and coding, but most payers, health systems, and billing companies expect it, and audit defensibility improves when coding is performed by credentialed staff.
CPC (Certified Professional Coder)
AAPC
Physician and outpatient professional coding
COC (Certified Outpatient Coder)
AAPC
Hospital outpatient and ASC coding
CIC (Certified Inpatient Coder)
AAPC
Inpatient facility coding and ICD-10-PCS
CRC (Certified Risk Adjustment Coder)
AAPC
Risk adjustment and hierarchical condition categories
CPB (Certified Professional Biller)
AAPC
Claims, denials, appeals, and revenue cycle
CCS (Certified Coding Specialist)
AHIMA
Hospital inpatient and outpatient coding
CCA (Certified Coding Associate)
AHIMA
Entry-level coding across settings
RHIT / RHIA
AHIMA
Health information management and data governance
How Do Audits Affect Medical Billing and Coding?
Audits test whether the documentation supports the codes billed and whether the payment received was correct. They come from several directions, and each has a different scope and consequence.
Internal audits: proactive chart reviews run by the practice or its billing partner to find and correct patterns before a payer does.
Payer and commercial plan audits: targeted reviews of high-volume or high-dollar codes, often focused on E/M level distribution, modifier 25, and modifier 59 usage.
Medicare contractor reviews: MAC targeted probe and educate reviews sample a small number of claims, provide education, and escalate if error rates persist.
Recovery audit and improper payment reviews: retrospective reviews that identify overpayments and underpayments for recoupment or correction.
OIG and program integrity investigations: the most serious tier, reserved for patterns suggesting systematic false claims.
The practical defense is the same in every case: complete documentation, codes supported by that documentation, a documented compliance policy, evidence of periodic internal auditing, and prompt correction and repayment when an error is found.
How EverCure Billing
Aligns Coding and Billing
EverCure Billing runs coding and billing as one connected workflow rather than two disconnected queues. Certified coders assign and validate codes against current ICD-10-CM and CPT releases and payer policy, billers submit and work the claim through to payment, and denial reason codes are routed back into coding and documentation feedback so the same denial does not repeat next month. Periodic internal audits document the accuracy of that process.
To request a coding and denial review for your practice,
contact EverCure Billing at info@evercurebilling.com or (929) 249-5929.
Frequently Asked Questions
About Medical Billing and Coding
One person can do both, and in small practices this is common. The trade-off is depth: a combined role rarely keeps pace with annual code updates, payer policy libraries, and denial analytics simultaneously. Separating the functions, or supplementing an internal biller with certified coding support, usually improves accuracy once volume grows.
Upcoding is reporting a higher-level or more expensive service than the documentation supports, which creates fraud and recoupment exposure. Downcoding is reporting a lower-level service than documented, which is not a fraud risk but permanently gives away legitimate revenue. Both are coding accuracy failures, and internal audits are designed to catch each.
Unbundling is billing individual component procedures separately when a single comprehensive code exists for the combined service. National Correct Coding Initiative edits are designed to detect it, and systematic unbundling is treated as a compliance issue rather than a clerical error.
Correctly coded claims are denied when the issue lies outside the code itself, such as inactive eligibility on the date of service, a missing prior authorization, an out-of-network provider record, a lapsed credentialing file, a coordination of benefits conflict, or a payer medical policy that does not cover the diagnosis-procedure pairing. Coding accuracy is necessary but not sufficient for payment.
ICD-10-CM updates take effect annually on October 1, and CPT updates take effect annually on January 1. HCPCS Level II codes update on a quarterly cycle, and payer medical policies change continuously throughout the year, which is why a scheduled code and policy update process matters as much as the annual releases.
Computer-assisted coding and natural language processing tools now handle a growing share of straightforward code suggestion, and CPT 2026 itself added codes recognizing augmented intelligence services in clinical care. In practice these tools shift coder work toward validation, complex cases, documentation improvement, and audit defense rather than eliminating the role, because responsibility for the code submitted still rests with the provider organization.
Need Help With Your Medical Billing and Coding?
EverCure Billing provides end-to-end medical billing, coding, and revenue cycle support for US healthcare practices. Contact us today for a free assessment.